This invention relates generally to clutch/brake mechanisms and more particularly to an enclosed clutch/brake unit which is specially constructed to minimize heat generation in order to avoid the adverse thermal effects that plague other enclosed units.
Combination clutch/brake units are used in a wide variety of applications, including many applications where it is highly desirable or even essential that the unit be enclosed. The clutch/brake unit includes friction linings on the clutch and brake disks, and it is necessary for the friction linings to be protected from grease and other materials that detract from their frictional capabilities. Units of this kind are commonly referred to as "dry" units as opposed to units which employ a cooling liquid in the housing. Consequently, in an operating environment where the clutch/brake unit is exposed to materials that can adversely effect the friction linings, the unit should be enclosed because the friction reducing materials can create operating problems until they are burned off or otherwise removed. For example, when used in food handling equipment which must be regularly washed for removal of food residues, the clutch/brake unit is exposed to greasy materials that can seriously detract from the ability of the friction linings to function properly. Thus, clutch/brake units that operate in this type of environment must be enclosed in order to properly function in a consistent manner.
When the brake is applied or the clutch is engaged, the pressure on the friction linings causes them to wear away. The dust that is thus generated during operation of the clutch-brake can contaminate the surrounding areas if it is allowed to escape from the unit. Therefore, in applications such as food handling or food processing and in other situations where contamination is intolerable, an enclosed clutch/brake unit is required since the dust that is generated must be adequately contained.
In these and other operating environments, enclosed clutch/brake units are highly desirable and in some cases are absolutely required. However, enclosed units are subject to problems that are not encountered by open units, most notably thermal problems. Considerable heat is generated when the brake is applied or the clutch is engaged and the friction linings slip with respect to the brake or clutch plates. Clutch slippage occurs each time the components are accelerated to operating speed and brake slippage occurs when they are stopped. These slippages create heat due to the effects of friction, and the heat is a particular problem in cyclical, start-stop process controllers which may cycle on and off 30-60 times per minute.
Open units can handle the thermal problems without great difficulty because cooling air can be passed through the unit and over the internal components to dissipate the heat. Usually, the rotor and clutch plates of an open unit are large diameter parts so that the torque capacity is high. Single friction surfaces and fin structures are common to provide a high heat dissipation capacity. However, an enclosed unit does not allow flow through it for dissipation of the heat, and thermal problems are much more prevalent in enclosed units than in open units.
When the brake and clutch disks are formed as separate parts, the brake disk is not loaded when the clutch is engaged. Consequently, backlash created by the fit of the spline teeth for the brake disk can result in rattling of the brake disk and the generation of objectionable noise during operation. Additional noise can be caused by unwanted contact of the brake disk when the clutch is engaged and contact of the clutch disk when the brake is engaged. Undue wear on the friction linings of the disks also results from this drawback in prior units.